US astronomers have found evidence of a star racing tightly around the monstrous black hole at the heart of our galaxy - the closest ever found near the matter-sucking body.

The scientists from the University of California, Los Angeles say the discovery will help them test Albert Einstein's theory of general relativity and his predictions of how black holes warp space and time.

The star, S0-102, is orbiting the black hole every 11.5 Earth years, much faster than the 60 years or longer orbit of most of the stars around the Milky Way's black hole centre.

It is only the second star discovered with such a short orbit - the other, S0-2, orbits the black hole every 16 years.

Lead researcher Andrea Ghez, who has been observing the black hole since she discovered it in 1998, says the find is thanks to improved imaging techniques.

She says the second data point is crucial for their research.

"It is the tango of S0-102 and S0-2 that will reveal the true geometry of space and time near a black hole for the first time," she said in a statement.

"This measurement cannot be done with one star alone."

Like Earth and other planets, both stars have elliptical orbits - meaning they regularly move closer and further from the black hole.

Ms Ghez and her team hope to see evidence of little wobbles in the orbit when the stars move closer, which would show they are being affected by the curvature of space time, as predicted by Einstein's theory.

She says it is "phenomenal" to find two stars so close to the black hole.

"This should not be a neighbourhood where stars feel particularly welcome," she said.

Black holes, which are what is left when a massive star dies and collapses in on itself, have a gravitational force so strong that even light cannot escape.

They cannot be seen directly and so are observed through their influence on the things around them.

"Now it's a whole new ball game," Ms Ghez said, adding that the team's investigations could open a new window into understanding black holes and how the universe evolves.

The research will be published in Friday's issue of the US journal Science.